Social affiliations play an important role in the onset and relapse of alcoholism and heavy drinking, yet this aspect of alcoholism and alcohol abuse has not been successfully modeled in rodents. Recently we developed the use of prairie voles (Microtus ochrogaster) to study negative (facilitating) and positive (inhibitory) social influences on alcohol consumption. Specifically, we demonstrated alcohol preference and heavy ethanol intake in this species, and showed that pair-housed prairie voles influence each other's drinking. When voles are introduced to alcohol in pairs they exhibit higher alcohol preference than when they are introduced to alcohol being single-housed. In these pairs, one vole influences (i.e., increases) alcohol consumption of its partner - modeling facilitating influences on alcohol drinking. In contrast, during pairing of high- and low-drinking voles that have previously experienced alcohol when they were single- housed, the vole with higher basal intake tends to decrease its drinking thereby matching its partner - modeling inhibitory social influences. Thus, the prairie vole could serve as the first rodent model of the effects of specific inter-personal affiliations on high alcohol drinking in both directions. We hypothesize that prairie voles influence their partner's rate of alcohol consumption via acoustic communication as do humans and that this influence is regulated by dominant/submissive relations, the opiate and the vasopressin (AVP) systems. We propose to test this hypothesis through following four Specific Aims. Specific Aim 1: To test whether the social influences on alcohol drinking occur by synchronizing alcohol drinking and are influenced by dominant-submissive interactions. Specific Aim 2: To test the whether USVs contribute to coordinated drinking in voles further increasing the validity of our model. Specific Aim 3: To test whether the efficacy of an established pharmacotherapy of alcoholism targeting the endogenous opiate system is modulated by social influences. Specific Aim 4: To test whether the AVP system known to regulate social affiliations in prairie voles contributes to regulation of coordinated drinking. Taken together this work will for the first time reveal information on the biological mechanisms regulating social influence on excessive alcohol drinking in a rodent model.